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820-00840 MacBook Pro 2017 board with USB data line issues

S

sekidata

Member
This A1708 board had extensive liquid damage, mostly in the USB-C and speaker circuitry area. I replaced several corroded components and restored some vias.

Now this board is at 20V USB-C, starting up, and functioning well, with the exception of USB-C data: any external USB drives are powered but not recognized. However, the startup manager (option key during restart) does recognize the external drives.

Where to start trying to restore full USB data functionality?
 
S

sekidata

Member
After poking around, I found that several protection diodes on USB data lines (D3306, D3310, D3314) were blown off the board. I traced these to shorts to ground on these lines:

USBC_XA_D2R_N<1>, USBC_XA_D2R_N<2>
USBC_XA_D2R_P<1>, USBC_XA_D2R_P<2>
USBC_XB_D2R_N<1>, USBC_XB_R2D_C_N<1>

These are only connected to the USB data controller U2800. Removing U2800 removed the shorts.
Replace U2800 and the redriver chip?
 
2informaticos

2informaticos

Administrator
Staff member
USB ports should work in basic mode, if redriver chip is good.
U2800 is needed only for thunderbolt options; like video out.
 
S

sekidata

Member
Ok, I removed U2800 for now. The redriver chip (PI3USB32) showed some minor corrosion, so I replaced it from a donor board. However, the situation is unchanged: external drives are only recognized during startup but not when OS is loaded.
 
S

sekidata

Member
Neither is recognized. I'd be happy getting USB 2.0 to work.

From the USB-C connector pinout, I understand that I need the center pins (D+, D-) to work, correct? They connect to the CD3215s via USBC_XA_USB_TOP_N and similar lines. What else needs to be working to establish functional USB 2.0 communication?
 
S

sekidata

Member
U2800 has been off the board for all tests since you stated that it is only needed for data such as video out.
 
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